Using this mail slot for my son has helped with getting the assignment out of the door in the morning and with him on the way to school.
Having it visible from several areas of the house, and near enough to his first entry area in the house helps a great deal as well.
A radio station tuned between channels and turned down low may create a good white noise base as well. He has an hour after getting home to relax and refocus, then one hour of study, and then just before bed he does a half-hour review during which we go over what he studied.
This helps reinforce what he learned and helps him to feel he has accomplished his work for the day.
A friend of mine found with her daughter that a white noise of ocean sounds and storm (thunder and rain) helped her child. Be willing to experiment, and when you find an atmosphere that seems to work, stick with it.
Some other suggestions to try would be electric fans in the room, which create an ambient white noise.
The skill of breaking tasks down into manageable segments is not something that comes naturally for ADHD children. Help your child learn this skill, so he can begin his work with a clear idea of what to do, and what to do next.
Go over the directions with her, read them aloud, do the first problem together, and then observe as she does the next by herself. Your support and praise are strong tools for your child; offer them when he puts forth good effort. Be helpful by pointing out a correction or two if you see the need, but be mindful of not ‘doing it for them’.
Having a place to study and a good environment to study in is great, but our children need more sometimes.
I find that general task assignments, such as ‘do your homework’, or ‘clean your room’ overwhelm my son quickly.